1. Field of the Invention
This invention relates to a finisher which gives such additional-workings as creasing, folding, punching, stapling and binding works to sheets discharged from such image forming devices as printers and copying machines. More particularly, this invention relates to a finisher which is provided with a sheaf-conveying unit which nips and conveys a sheaf of sheets temporarily stacked and aligned in a receiving tray unit.
2. Description of the Related Art
Recently, various finishers, which give various additional-workings to sheets with an image formed surface which are outputted from such image forming devices as printer and copying machines, have been proposed. The term "additional-workings" as used herein means various working processes such as sorting sheets, stapling sheets, folding sheets in two (double-folding), creasing sheets (creasing), or folding sheets in a cross section like a letter Z (Z-folding), binding sheets with mucilage, and punching sheets for filing. The finisher generally is provided with a receiving tray unit for temporarily storing such sheets as have been folded and punched. The sheaf of sheets, which has been stacked and aligned in the receiving tray unit, is conveyed to a stapler and is stapled.
The finisher is further provided with a regulating device disposed on the receiving tray unit as projected. The regulating device contacts a leading end of the sheaf, which falls on the leading end side when the sheaf is conveyed toward the stapler, in order to adjust the leading end of the sheaf.
In a number of the conventional finishers, conveyance of a sheaf for stapling is performed by actuating a chuck unit for nipping a sheaf stacked and aligned in the receiving tray unit, and generating a movement of the chuck unit toward the stapler (U.S. patent application Ser. No. 08/633,452).
The sheets, which are received in the receiving tray unit, are slightly curled under the influences of heat and pressure during the image formation. The conventional finisher forces the leading end of the sheaf to contact the regulating device for alignment without regard to the curl in the sheets.
It possibly results in completing the alignment in a state that some leading edges of the sheets ride aslant on the regulating device, thus the sheets of sheaf is stapled having the misalignment or deviation relative to the coveying direction. The misalignment will naturally impair the appearance of the stapled sheaf.
Provision of such retaining devices as disclosed in U.S. Pat. No. 4,852,867 and Japanese Laid-Open Patent Application No. 57-72537 is conceivable for adjusting the deviation of the sheet conveying direction caused by the curls in the sheets. However, it entails the addition of another mechanism different from the sheaf conveying mechanism and results in complicating the construction and boosting the cost.